As compositions for electrical or electronic part material, various curable resins are used for a wide range of uses. For example, epoxy resin, imide resin, amideimide resin, unsaturated polyester resin, phenolic resin and other curable resins are used for: semiconductor-sealing resin; impregnating resin for spinning, electrically insulating varnish; insulating material for a printed wiring board; impregnating resin for a printed wiring board; a coating agent for an electronic component; a conformal coating article; a potting agent for an electronic component; an adhesive for an electrical or electronic component; a compound for radiating heat from an electronic component; and the like. However, these resins have, for example, problems that cured products of the resins are hard, and the products cause the bonding wires to be cut because of a difference in linear expansion coefficient therebetween, and produce other bad effects. As a polymer which gives a rubbery curable resin and does not have these problems, known are, for example, silicone polymer, polyether polymer, hydrocarbon polymer, vinyl polymer and the like that are each a polymer having a hydroxyl group or a hydrolyzable group bonded to a silicon atom, and having at least one silicon-containing group which is to form a siloxane bond to be crosslinkable (hereinafter, the silicon-containing group may be referred to as the crosslinkable silyl group). The curing of these polymers is characterized in that heating is not necessarily required for the curing since the curing is based on the condensation reaction of the crosslinkable silyl groups, but has common problems, for example, slow curing speed, insufficient depth-curability and the like.
As polymers without these problems, silicone, polyether and hydrocarbon polymers have been suggested. The silicone polymers have problems about electrical properties thereof (see Patent document 1); thus, for example, a low-molecular-weight silicone compound present in the cure product causes an electrical contact-point hindrance. The polyether polymers, and unsaturated ones of the hydrocarbon polymers may be poor in heat resistance. Saturated ones of the hydrocarbon polymers themselves are high in viscosity to cause a problem about handleability. The inventors reported polymers whose main chains are vinyl polymers obtained by living radical polymerization and which respectively have at a terminal thereof a (meth)acryloyl group (Patent documents 2 to 4). Although cured products of these polymers are excellent in, for example, heat resistance and oil resistance, the products have problems about electrical insulation, and resistance to discoloration of electrodes. Thus, the products may not be used for sealing electrical members, or as adhesives.